Calling Sequence

Arguments

a string equal to "linear" (or "l") for linear or piecewise linear treatment
or "constant" (or "c") for constant treatment.

bp

the breakpoints to provide if you want a piecewise linear treatment.

y

output, the signal x with the trend removed from it.

Description

This function removes the constant or linear or
piecewise linear trend from a vector x. In general
this can be useful before a fourier analysis. If x is
matrix this function removes the trend of each column of x.

When flag = "constant" or "c" detrend removes the constant trend
(simply the mean of the signal) and when flag = "linear" or "l" the function
removes the linear trend. By adding a third argument bp it is possible to
remove a continuous piecewise linear trend. Note that the "instants" of the signal
x goes from 0 to m-1 (m = length(x) if x is a vector and m = size(x,1) in case
x is a matrix). So the breakpoints bp(i) must be reals in [0 m-1]
(breakpoints outside are simply removed from bp vector).

The trend is got by a least square fit of x on the appropriate function space.